1. Field of the Invention
The present invention relates to a twisted pair cable for communication of high speed signals, such as a local area network (LAN) cable. More particularly, the present invention relates to a twisted pair cable having an asymmetrical insulation layer on one or more insulated conductors of a twisted pair of the LAN cable.
2. Description of the Related Art
FIG. 1 shows a cable 1 with a jacket 7, in accordance with the background art. The cable 1 has a first twisted pair 11, a second twisted pair 13, a third twisted pair 15, and a fourth twisted pair 17. Each twisted pair includes two conductors. Specifically, the first twisted pair 11 includes a first insulated conductor 19 and a second insulated conductor 21. The second twisted pair 13 includes a third insulated conductor 23 and a fourth insulated conductor 25. The third twisted pair 15 includes a fifth insulated conductor 27 and a sixth insulated conductor 29. The fourth twisted pair 17 includes a seventh insulated conductor 31 and an eighth insulated conductor 33.
Each of the first through eighth insulated conductors 19, 21, 23, 25, 27, 29, 31 and 33 is constructed of an insulation layer surrounding an inner conductor, as best exemplified in the cross sectional view of FIG. 3. The outer insulation layer may be formed of a flexible plastic material having flame retardant and smoke suppressing properties. The inner conductor may be formed of a metal, such as copper, aluminum, or alloys thereof.
As illustrated in FIG. 1, each twisted pair 11, 13, 15 and 17 is formed by having its two insulated conductors continuously twisted around each other. For the first twisted pair 11, the first insulated conductor 19 and the second insulated conductor 21 twist completely about each other, three hundred sixty degrees, at a first interval w along the length of the cable 1. The first interval w may purposefully vary within a first range of values (randomly or in accordance with an algorithm) along the length of the cable 1.
For the second twisted pair 13, the third insulated conductor 23 and the fourth insulated conductor 25 twist completely about each other, three hundred sixty degrees, at a second interval x along the length of the cable 1. The second interval x may purposefully vary within a second range of values (randomly or in accordance with an algorithm) along the length of the cable 1.
For the third twisted pair 15, the fifth insulated conductor 27 and the sixth insulated conductor 29 twist completely about each other, three hundred sixty degrees, at a third interval y along the length of the cable 1. The third interval y may purposefully vary within a third range of values (randomly or in accordance with an algorithm) along the length of the cable 1.
For the fourth twisted pair 17, the seventh insulated conductor 31 and the eighth insulated conductor 33 twist completely about each other, three hundred sixty degrees, at a fourth interval z along the length of the cable 1. The fourth interval z may purposefully vary within a fourth range of values (randomly or in accordance with an algorithm) along the length of the cable 1.
Each of the twisted pairs 11, 13, 15 and 17 has a respective first, second, third and fourth mean value within the respective first, second, third and fourth ranges of values. Each of the first, second, third and fourth mean values of the intervals of twist w, x, y and z may be unique, e.g., different from the other three values. More information about the cable 1 of the background art can be found in the Assignee's U.S. Pat. No. 6,875,928 and published U.S. Application 2008/0073106, which are incorporated herein by reference.
The first through fourth twisted pairs 11, 13, 15 and 17 may be separated by a star-shaped or plus-shaped separator 35 or separated from one another by a tape separator 35 or a multiplicity of tape separators 35 and may be wound together with the separator 35 in a direction 39 to form a twisted core. The core twist direction 39 may be in the same direction as the pair twist directions of the first through fourth twisted pairs 11, 13, 15 and 17.
FIG. 2 is a close-up view of the first twisted pair 11. FIG. 3 is a cross sectional view taken along line III-III in FIG. 2. FIGS. 2 and 3 illustrate that the first insulated conductor 19 would be formed by a first conductor 41 with a diameter D1 of about twenty-three gauge size, surrounded by a uniform layer of a first dielectric insulating material 43 having a radial thickness T1 of about eleven mils. Likewise, the second insulated conductor 21 would be formed by a second conductor 45 with a diameter D2 of about twenty-three gauge size, surrounded by a uniform layer of a second dielectric insulating material 47 having a radial thickness T2 of about eleven mils. Hence, the spacing S1 between the center of the first conductor 41 and the center of the second conductor 45 would be about 45 mils.